Effect of lesion volume on cerebral hemodynamics after focal brain injury and shock.

Cerebral blood flow (CBF) varies unpredictably in patients after head injury and hemorrhagic shock. Proper treatment requires knowledge of ischemic versus hyperemic flow. The degree to which the size or severity of the injury may contribute to CBF abnormalities is unknown. We hypothesized that lesion size is a determinant of postinjury CBF. We measured cerebral and systemic variables in a porcine model of focal cryogenic brain injury and hemorrhagic shock over a 5-hour period. Swine were randomized to receive either a large or small lesion followed by hemorrhage. In the small lesion group traumatic brain injury, followed by shock and resuscitation, produced a significant and sustained elevation in bihemispheric regional CBF and cerebral oxygen delivery that was significantly greater than that observed in either the large lesion group or the controls (p < 0.05). There were no significant differences between the experimental groups in volume of hemorrhage, intracranial pressure, cerebral perfusion pressure, arterial oxygen content, or PaCO2. These data suggest that the volume of injured tissue may determine post-resuscitation CBF, and that interventions to reduce cerebral blood volume (i.e., hyperventilation) may not be universally applicable in all head injured patients.